Frost after-effects Seedling disease in stressed rice

With some exceptions, the Arkansas rice crop fared well considering the below-freezing weather that damaged many other crops around Easter. However, one rice expert has recently become concerned over the severity of pythium seedling disease that has shown up.

“It has really shown up fairly widespread,” said Chuck Wilson, Arkansas Extension rice specialist. “I think the rice being stressed from the freeze and the cold weather that followed it caused pythium to show up.”

Wilson said a number of fields that a few days earlier appeared fine were dying.

“The majority of the crop will survive, but more acreage than I had originally thought will have to be replanted because of seedling disease.”

Wilson expects Arkansas rice farmers to plant 1.2 million acres of rice this year, 13 percent lower than last year and the lowest acreage since 1996.

“The main reasons for the decrease include extremely high input costs across the board, lack of adequate pricing opportunities and lack of seed availability,” said Bobby Coats, Arkansas Extension economist.

A planting restriction on CL 131 and Cheniere varieties this year prompted widespread concern about seed supply, Wilson noted. “According to my sources, the overall amount of available seed is more than enough to plant the crop. However, that doesn't mean there is enough of every variety. Because of the supplies, farmers may not have as many choices for a specific variety, particularly for fields that have to be replanted.”

The latest recommended seeding rate for most varieties is 30 seeds per square foot to achieve a stand of 15 to 20 plants per square foot, Wilson said. Since the seed size differs among varieties, the actual seeding rate in pounds per acre varies by variety.

“Our long-standing recommendation has been to plant 40 seeds per square foot hoping to achieve a population of 15 to 20 plants per square foot. However, research shows we can achieve this stand density with optimum yields by reducing the seeding rate by about 25 percent.

“One thing to keep in mind about seeding rates is the availability of Icon insecticide to control lespedeza worm. Since Icon will soon be unavailable on the market, other cultural practices may be necessary.”

One way to overcome injury before Icon came on the market was to use higher seeding rates.

“We recommend increasing the seeding rate by 40 percent if the field has a history of heavy grape colaspis injury,” Wilson said.

Chemical control outside of Icon is limited. Mustang Max is labeled for preventive suppression of grape colaspis when applied at 4 ounces per acre between 10 days prior to planting and five days after planting. The effectiveness of this application has not been confirmed in university trials, but will be the only chemical control option for 2007.

An Arkansas Extension publication — Rice Information Sheet 163 — will soon be available to help calculate seeding rates for specific varieties and will also be available in a computer program at riceseed.uaex.edu.

Wilson also recommends soil sampling to ensure that farmers are applying adequate amounts of fertilizer in fields that need it and not applying it where it's not needed.

He said potassium, or potash, should be looked at carefully. “Deficiency of potassium can rob yields and you may never know it.”